I'm usually pretty sporatic when it comes to vc purchases. I've had cards when they first come out and have paid rediculous prices, other times my urge drops off and I can live off of a $15-$30 vc like a Riva128 or my latest budget gamer, the Voodoo5.
Also depends on what other components I have in the system at that very moment. If I know I'll be needing funds soon and end up ridding of stuff, then I'll be more likely to stick with something very lowend. But when I'm in the process of upgrading, I'll be more willing to spend a bit more on a vc I like.
Most ever spent on a vc was $460Cdn. Most I will ever spend is prolly $600Cdn max, but $300-$350Cdn is a more realistic figure.